Annealing Temperature Range Research Articles

Constituent Isomerism-Induced Quasicrystal and Frank–Kasper σ Superlattices Based on Nanosized Shape Amphiphiles

Naturally, subtle variations in the chemical structures of constituent molecules may significantly affect their multiscale spatial arrangements, properties, and functions. Deceptively simple spheri...

A Facile Route to Synthesis of Ferromagnetic and Antiferromagnetic Phases of Iron Oxide Nanoparticles by Controlled Heat Treatment of Ferritin

Magnetic nanoparticles of ferromagnetic and antiferromagnetic phases were synthesized from controlled heat treatment of dry ferritin powder in a bottom-up approach. Heat treatment paves the way for synthesis of Fe2O3 solid phase from iron molecular complexes stored in the cavity of ferritin; the strong increase (~ 150 times) in saturation magnetization is a sign of the presence of ferromagnetic exchange coupling which exists only in solid phase. In this experimental study, vibrating sample magnetometer (VSM) was used to study magnetic induction. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed for analysis of structure and morphology of the samples. Differential scanning calorimetry (DSC) was used to search for indicators of structural phase transformation through scanning of temperature. The nanoparticle size with highly narrow distribution (mean size ~ 6 nm) was observed by SEM for sample annealed at 430 °C. As indicated by XRD measurements, the majority phase of Fe2O3 nanoparticles was amorphous up to 500 °C, whereas DSC demarcates the crystalline phase transition temperature at 545 °C. The annealing temperature range from 400 to 500 °C was found to be suitable for growing ferromagnetic nanoparticles endowed with high saturation magnetization and low coercivity. At higher range of annealing temperature (500–700 °C), XRD confirms the presence of α-Fe2O3 (haematite) phase which is an antiferromagnetic crystalline system with weak magnetization. A systematic decline of magnetization on increasing the annealing temperature beyond 500 °C was attributed to finite size effects and increased purity of antiferromagnetic phase.

Comparative study of V and Mo on the glass formation and magnetic properties of Fe-Si-B-Cu-Nb-M (M=V, Mo) nanocrystalline for high frequency applications

This paper aimed at improving high-frequency magnetic properties and decreasing material cost of “Finemet”alloy without sacrificing saturation magnetization (Ms) and coercivity (Hc) by minor V and Mo substitution of Nb. Both V and Mo enhanced glass forming ability (GFA) and promoted the precipitation of primary α-Fe particles. Meanwhile, V addition hindered the precipitation of the secondary phase and consequently extended annealing temperature range. After annealing, the Fe73.5Si15.5B9Cu1Nb2V1 and Fe73.5Si15.5B9Cu1Nb2.5Mo0.5 have high Ms of 129.0 and 127.6 emu/g, low Hc of 2.7 and 5.3 A/m, and high μe of 3.6 × 104 and 3.4 × 104 at 200 kHz/0.3V respectively. The order of the effect of Nb, Mo and V on decreasing grain size and coercivity (Hc) is Nb>V>Mo. Besides, the increasing electrical resistivity via adding 1.0 at.% V and 0.5 at.% Mo contributed to a higher and more stable effective permeability (μe) in a wide high frequency range. These advantages for soft magnetic materials are promising for high-frequency applications.

Post-annealing temperature-dependent electrical properties of thin-film transistors with a ZnO channel and HfOx gate insulator deposited by atomic layer deposition

Electrical properties of an oxide semiconductor thin-film transistor (TFT) with a ZnO channel layer and a HfOx gate insulator, both of which are deposited by atomic layer deposition (ALD), are investigated at varying post-annealing temperatures. The TFTs that are post-annealed at 250 and 300 °C show relative low on/off ratios < 102. They also have a counter-clockwise hysteresis in the transfer curves with slightly reduced threshold voltage upon repeatedly applying a positive gate voltage. However, the transfer curves of the devices post-annealed at 350 °C exhibit the increased on/off ratios > 102 and clockwise hysteresis with a little increased threshold voltage due to electron charging at the trap states in the HfOx/ZnO interface or inside the HfOx gate insulator. The threshold voltage shift, however, is negligible at the gate voltage of +20 V and as low as about 2.2 V at the highest gate voltage of +40 V, which guarantees stable operations of TFTs without significant degradation of electrical performance. The channel mobilities are around 4.0 cm2 V−1 s−1 at this annealing temperature range. The presented results report the dependence of electrical performance such as on/off ratio and electrical instability, possibly caused by electrical charging, on the post-annealing temperature, which requires post-annealing at 350 °C or higher temperatures for stable operations of TFTs with ALD-ZnO and HfOx.

Intrinsic properties of high-aspect ratio single- and double-wall anodic TiO2 nanotube layers annealed at different temperatures

In this work, we present the influence of thermal annealing on morphological, structural, electrical, optical, and photoelectrochemical properties of double- (DW) and single-wall (SW) TiO2 nanotube (TNT) layers. High-aspect ratio TNT layers with a thickness of ∼5 μm and ∼20 μm with an average inner diameter of ∼250 nm and ∼130 nm, respectively, were prepared via electrochemical anodization of Ti foil in two different fluoride containing ethylene glycol-based electrolytes. The inner wall of the native DW TNT layers was quantitatively removed via a mild pre-annealing followed by a selective etching treatment in piranha solution, yielding SW TNT layers. The obtained SW TNT layers annealed at 300–500 °C possess enhanced conductivity by 1–2 orders compared to their DW counterparts. The photoelectrochemical properties of SW TNT layers are enhanced compared to their DW counterparts in the annealing temperature range 300–800 °C. In principle, the SW TNT layers could be potentially favored to the DW TNT layers in electrical and photoelectrochemical applications due to their more superior intrinsic properties.

Control of Oxygen Vacancies in TiO6 Octahedra of Amorphous BaTiO3 Thin Films with Tunable Built‐In Electric Field in a‐BaTiO3/p‐Si Heterojunction for Metal–Oxide–Semiconductor Applications

Amorphous BaTiO3 (a‐BTO) thin films are deposited on p‐Si(111) substrates by radio frequency (RF) magnetron sputtering without extra substrate heating. The microstructure of a‐BTO thin films is modified by postannealing at low temperatures (260–600 °C) in air. The results show that distorted TiO6 octahedra exist in a‐BTO thin films, and the degree of distortion decreases when the annealing temperature rises. The concentration of O vacancies in the TiO6 of the thin films remains high when postannealed between 370 and 460 °C, and a built‐in electric field across the a‐BTO/p‐Si heterojunction is established in this annealing temperature range. This built‐in electric field is regulated by controlling the concentration of O vacancies from the TiO6. The tunable C–V characteristic of the Au/a‐BTO/p‐Si metal–oxide–semiconductor (MOS) capacitor is obtained by modulating the built‐in electric field at the heterojunction, and the flat band voltage of the MOS capacitor shifts from about −3 V to at least −13 V when the postannealing temperature increases from 260 to 420 °C. This kind of tunable built‐in electric field at the a‐BTO/p‐Si heterojunction, controlled by modifying the microstructure of amorphous oxide thin films, has never been observed before, which will be useful for MOS applications.

The self-repairing of ion irradiation damaged Mo–S–Ti (MoST) lubricant films by thermal annealing

Mo–S–Ti composite films deposited by magnetron sputtering were irradiated by 2 MeV Au2+ with a high fluence of 3.3 × 1015 ion cm−2. Upon intense bombardment by 2 MeV Au2+, the Mo–S–Ti thin film exhibits sensitivity to radiation-induced amorphization at room temperature. Afterwards, thermal annealing experiments on the irradiated thin films were conducted over the temperature range of 200 °C–900 °C. Subsequent annealing experiments found that the effect of heavy ion irradiation on Mo–S–Ti films was a reversible reaction, with the irradiation-damaged MoS2 lattice being completely self-repaired by thermal annealing. In the annealing temperature range of 200 °C–600 °C, no evidence of an amorphous to recrystallized transition was observed. When the temperature was increased to as high as 700 °C, the damaged MoS2 molecules were well recrystallized. HRTEM images of irradiated samples annealed at 700 °C strikingly found that the self-repaired MoS2 crystallites preserving long range ordering were still rearranged in an intrinsic (0 0 2) crystal orientation. MoS2 nanocrystals that survived the ion bombardment step may provide some nucleus for subsequent MoS2 grains growing dominantly in the (0 0 2) direction in thermal annealing. Compared with the difficult recrystallization in thermal annealing, the irradiation-amorphized MoS2 phases were easily self-repaired under friction. The low transition potential barrier from irradiation-induced amorphization to crystallization, achieved by mechanical working, may be an important reason for the quick recrystallization.

Crystallization and magnetic hardening behaviour of Fe-rich FeSiBNb(Cu) melt-spun alloys

The sequential, multi-stage crystallization and magnetic hardening behaviour of Fe82B14Si2Nb2, Fe83B13Si2Nb2, Fe83B12Si2Nb2Cu1 and Fe85B13Nb2 melt-spun alloys have been investigated. The microstructure-crystallization-magnetic property relationship was established using X-ray diffractometry (XRD), differential scanning calorimetry (DSC), magnetometry, transmission electron microscopy (TEM) and magneto-optical Kerr effect microscopy (MOKE) techniques. The increase of Fe content (>82 at%) of as-quenched ribbons imparts microstructural heterogeneity across the ribbon cross–section; i.e., textured α-Fe crystals at the free surface to hetero-amorphous microstructure in the bulk matrix. The isochronal annealing of hetero-amorphous alloys depicts simultaneous surface and bulk crystallization process occurring before and after the crystallization onset temperature (Tx1) temperature. The annealing temperature range (Ta < Tx1) coinciding with the paramagnetic region of the thermo-magnetic plot, induces irreversible magnetic hardening due to simultaneous coarsening of pre-existing crystal nuclei and exchange de-coupling between nanocrystal and intergranular matrix. The onset of primary crystallization in the pre-crystallized ribbons results in bimodal nanocrystallite distribution having an average crystallite size exceeding the ferromagnetic exchange length of Fe-based alloys. The minor Cu addition alters the growth morphology of pre-existing nuclei from dendrite-like to equiaxed, assisting heterogeneous nucleation and improving intergranular amorphous stability by delaying boride precipitation. The soft-magnetic property deterioration of partially crystallized ribbons is discussed within the framework of Extended-Random Anisotropy models.

Size control of GaN nanocrystals formed by ion implantation in thermally grown silicon dioxide

The growth of GaN nanocrystals in an amorphous SiO2 matrix by sequential Ga and N implantation and rapid thermal annealing is reported. The effect of the implantation and annealing conditions on the distribution of the implanted ions, as well as the size, static disorder, and stability of the grown GaN nanocrystals, is studied by means of transmission electron microscopy, Rutherford backscattering spectrometry, Raman scattering, and extended X-ray absorption fine structure spectroscopies. It is found that the optimum temperature range for the post-implantation annealing of the nanocrystals, with a size that ranges from about 3 to 12 nm, is 1000–1100 °C. Higher temperatures result in the dissociation of the nanocrystals and out-diffusion of N and Ga, whereas lower temperatures are insufficient for the growth of GaN nanocrystals. Annealing for 30–90 s is optimum in order to avoid considerable loss of N and Ga. However, upon annealing at higher temperatures within the optimum range, up to 1100 °C, or for longer times, up to 120 s, larger GaN nanocrystals are grown and/or lower static disorder is observed.

Annealing temperature dependence of optical and structural properties of Cu films

Annealing temperature dependency of the optical and structural properties of Cu films is carefully studied using multiple means such as spectroscopic ellipsometry, x-ray diffraction, white-light interferometry, atomic force microscopy, scanning electron microscope (SEM), and the four-probe method. A wide annealing temperature range from 300 to 1200 K is examined experimentally. We find that the optical and structural properties of Cu films annealed at above 600 K cannot be naturally extended from the data commonly achieved on the samples annealed at the temperature below 600 K. When the annealing temperature is increasing, two transition points at around 600 and 900 K have been found by the Drude-Tauc-Lorentz analysis of the dielectric functions covering the energy range from 0.73 to 6.42 eV. The transition feature at 600 K can be attributed to the improvement of the crystalline state caused by annealing, which can be interpreted by the sharper diffraction peak shown in x-ray diffraction (XRD). The transition feature at 900 K was caused by the emergence of island structure due to the high-temperature annealing, which was supported by the SEM images as well. In fact, both the conspicuous scattering characteristics in the pseudodielectric function and the spurious peaks in the XRD pattern indicate the dramatically morphologic changes induced by the migration and reaggregation of Cu nanoparticles. The downward trend of dc resistivity captured in dielectric function analysis was supported by that of the sheet resistivity measured by the four-probe method.

FeCo– Fe2CoO4/Co3O4 nanocomposites: Phase transformations as a result of thermal annealing and practical application in catalysis

The results of the synthesis and subsequent phase transformations of FeCo nanowires depending on the annealing temperature are presented. An annealing temperature range of 200–800 °C was chosen to initialize the processes of annihilation of point defects at low temperatures, as well as phase transformations as a result of oxidation of nanostructures at high annealing temperatures. In the course of the research, a three-stage process of phase transformations was established, accompanied by oxidation of the structure followed by the formation of oxide phases of the spinel type Fe2CoO4 and Co3O4. It was found that at temperatures of 400 °C and 600 °C, the introduction of oxygen occurs nonuniformly along grain boundaries with the subsequent formation of oxide compounds, and in the case of annealing at a temperature of 800 °C, the oxygen distribution in the structure of nanowires becomes uniform, which indicates the complete oxidation of nanowires with isotropic the formation of oxide phases in the entire volume of nanowires. The prospects of using oxide biphasic nanowires for catalytic reduction reactions para-nitroaniline - para-phenyldiamine are shown.

Influence of high-temperature annealing on the characteristics of fast electron-irradiated p-n-structures based on neutron doped silicon

The investigation results of the annealing influence (Тann = 300–800 ºС) on the minority charge currier lifetime tP in the n-base of p-n-structures, manufactured on the base of neutron transmutation doped silicon (NTD) КОФ300, irradiated at room temperature by different fluences (F = 1 · 1014 – 3 · 1016 cm–2) of electrons with the energy of Еe = 4 MeV are presented. It is established that at low electron fluences (F = 1 · 1014 cm–2), the annealing of minority charge currier lifetime tP in the n-base of p-n-structures occurs in two stages: the first – 320–400 ºС and the second – 550–650 ºС. At higher electron fluences (F = 5 · 1015–2 · 1016 cm–2), three annealing stages occur: the first – 400–450 ºС, the second – 520–650 ºС and the third – 710–770 ºС. At this, the structure barrier capacitance C dependences on Тann at high electron fluences show the geometry capacitance up to the annealing temperatures Тann = 400 ºС. In the annealing temperature range of Тann = 420–570 ºС, the increase in С with maximum is seen at Тann = 480 ºС and a subsequent decrease in the geometry capacitance is seen in the annealing temperature range of Тann = 600–670 ºС, and then again the increase in С occurs in the annealing temperature range of Тann = 720–770 ºС reaching the С values corresponding to those of the non-irradiated samples in the annealing temperature range of Тann = 770–800 ºС. The analysis of the DLTS-spectra of the investigated structures has allowed establishing the formation in the annealing process of the deep acceptor level ЕС – 0.68 eV at Тann &gt; 400 ºС, the deep donor level ЕС – 0.32 eV in the annealing temperature range of Тann = 420–570 ºС and the deep acceptor level ЕС – 0.53 eV at Тann &gt; 700 ºС, which satisfactorily explains the dependences of t P and С on Тann obtained in this paper.

Low dielectric loss induced by annealing in (La0.5Nb0.5)0.005Ti0.995O2 colossal permittivity ceramics

Low dielectric loss (tanδ 104) (La0.5Nb0.5)0.005Ti0.995O2 ceramics. The effects of annealing on two important dielectric relaxations, electron-pinned defect-dipole (EPDD), and Maxwell–Wagner polarization were explored. An enhancement of activation energy (Ea) value and a large distribution of relaxation time τ were detected in EPDD relaxation for the ceramics annealed at 1123 K. The EPDD polarization was destroyed, accompanied by the disappearance of CP in the high annealing temperature range (> 1273 K). Impedance spectroscopy analysis suggested that grain boundary impedance could greatly enhanced as the ceramics were annealed at 1123 K. Strong electrode-material-dependent dielectric properties were detected, and a high tanδ was observed after the insulating surface layer was removed. The CP and low tanδ were ascribed to the maintenance of EPDD polarization, the enhancement of grain boundaries resistance, and the formation of an insulating surface layer through appropriate annealing.

Thermal annealing effects of InGaAs (1.0 eV) and InGaAs (0.7 eV) sub-cells of inverted metamorphic four junction (IMM4J) solar cells under 1 MeV electron irradiation

In this work, thermal annealing effects of InGaAs (1.0 eV) and InGaAs (0.7 eV) sub-cells for inverted metamorphic four junction (IMM4J) solar cells after being irradiated by 1 MeV electrons are investigated by using light &lt;i&gt;I&lt;/i&gt;-&lt;i&gt;V&lt;/i&gt; characteristic, dark &lt;i&gt;I&lt;/i&gt;-&lt;i&gt;V&lt;/i&gt; characteristic and spectral response. Annealing temperature range is 60–180 ℃ and annealing time is 0-180 min. The results indicate that the open-circuit voltage &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;oc&lt;/sub&gt;, short-circuit current &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;sc&lt;/sub&gt;, and maximum power &lt;i&gt;P&lt;/i&gt;&lt;sub&gt;max&lt;/sub&gt; of two sub-cells are gradually recovered with annealing time increasing, and the rate of recovery increases with annealing temperature increasing. Besides, the recovery rate of InGaAs (1.0 eV) sub-cell is less than that of InGaAs (0.7 eV) sub-cell under the same annealing temperature and time. Double exponential model is used to fit the dark &lt;i&gt;I&lt;/i&gt;-&lt;i&gt;V&lt;/i&gt; curve for the key parameters (the serial resistant &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt;, the parallel resistant &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;sh&lt;/sub&gt;, the diffusion current &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;s1&lt;/sub&gt; and the recombination current &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;s2&lt;/sub&gt;). It is found that &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt;, &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;s1&lt;/sub&gt; and &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;s2&lt;/sub&gt; of two sub-cells decrease gradually and &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;sh&lt;/sub&gt; increases during annealing and the rate of recovery increases with annealing temperature rising. However, the recovery of &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;s1&lt;/sub&gt; and &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;s2&lt;/sub&gt; of InGaAs(1.0 eV) are much greater than that of InGaAs(0.7 eV). The equivalent model between short-circuit current density (&lt;i&gt;J&lt;/i&gt;&lt;sub&gt;sc&lt;/sub&gt;) and defect concentration (N) induced by irradiation and annealing is established. &lt;i&gt;N&lt;/i&gt; changes follow the first reaction kinetics, and the rate constant follows the Arrhenius equation with the annealing temperature. Therefore, the thermal annealing activation energy of InGaAs(1.0 eV) and InGaAs(0.7 eV) sub-cells are 0.38 eV and 0.26 eV, respectively. These efforts will contribute to the IMM4J solar cells, in particular, to space-based applications.

Rapid thermal annealing on the atomic layer-deposited zirconia thin film to enhance resistive switching characteristics

The resistive switching random access memory (RRAM) device has received a great interest for the next-generation non-volatile memory application, and resistive switching (RS) characteristics are mainly affected by conductive oxygen vacancies ([V··]) within switching material. Various effective approaches with materials, doping, and thermal treatments have been attempted to achieve the stable RS behaviors. Particularly, thermal annealing is considered as an efficient knob to control [V··] compared to other approaches. However, research on thermal treatment still lacks results and further research efforts are still needed to improve the RS characteristics of the devices. In this work we investigated the RS characteristics of Ti/ZrOx/Pt-structured RRAM device in comparison without and with postrapid thermal annealing (RTA) temperature range under oxygen ambient. The as-fabricated device with atomic layer-deposited ZrOx switching layer exhibited conducting characteristics, which is related to a relatively high amount of [V··] within switching medium. It indicates that moderate amount of [V··] apparently determines the appropriate RS behaviors. With this regard, we modulated the [V··] in ZrOx thin films by employing RTA in the ranges of 500 °C to 800 °C at the oxygen ambient for 60 s. Unlike device without RTA, we observed the stable RS characteristics from device with RTA and device annealed at 700 °C exhibits the excellent bipolar RS characteristics such as higher Ron/Roff, smaller cycle-to-cycle switching variation, better endurance, and longer retention among RTA conditions, indicating moderate amount of [V··] formed within ZrOx thin film layer. Moreover, increasing ALD ZrOx thickness shows the further improvement in the RS characteristics and RTA on the thicker ZrOx device still improves the RS behaviors. This research indicates that modulating [V··] by fast thermal annealing on the ALD zirconia material can provide the proper RS characteristics of the non-volatile memory applications.

High-temperature microstructural evolution of SiCN fibers derived from polycarbosilane with different C/N ratios

Research into the high-temperature microstructural evolution of SiCN ceramic fibers is important for the aerospace application of advanced ceramic matrix composites in harsh environments. In this work, we studied the microstructural evolution of SiCN fibers with different C/N ratios that derived from polycarbosilane fibers at the annealing temperature range of 1400∼1600 °C. These results showed that the phase separation of SiCxNy phase and the two-dimension grain growth process of free carbon nanoclusters could be processed at the researched temperature range. As the annealing temperature increased to 1600 °C, the crystallization of amorphous SiC and Si3N4 could be detected. SEM and Raman analysis showed that the decomposition and carbothermal reduction of the Si3N4 phase at high temperatures played primary roles in contributing to the fiber strength degradation. Thus, a higher C/N ratio, which is beneficial for inhibiting the decomposition of amorphous Si3N4, helps SiCN fibers retain high tensile strength at high temperatures.

A Growth Kinetics Study and Simulation for Recrystallized Ferrite Grains under the Annealing of Automotive Steel Cold-Rolled Sheets

The study results show the normal growth of recrystallized ferrite grains under the isothermal annealing of cold-rolled sheets made of five automotive steels (DX54D, HX260YD, CR210B2, 08ps, HX300LAD) obtained using a Gleeble 3800 experimental system. Based on the obtained data, a mathematical model of this process has been developed. The simulation results obtained for the kinetics of ferrite grain growth in a practically important annealing temperature range agree well with the experimental data.

Structural and optical characterization of the crystalline phase transformation of electrospinning TiO2 nanofibres by high-temperatures annealing

The electrospinning technique has been used to synthesize TiO2 nanofibres, which by annealing at high temperatures in a wide range achieves the crystal phase transformation of anatase to rutile passing through the anatase+rutile mixed. The investigated temperature range was 0-1000°C. The TiO2 nanofibres chemical stoichiometry and surface morphology were obtained by Scanning Electron Microscopy and Energy Dispersive Spectrometry. The nanofibres diameter was ranged from 137.0 to 115.3 nm in the annealing temperature interval of 0-1000°C. The influence of the annealing temperature on the structure and crystal phase quality of the TiO2crystal has been investigated by X-ray diffraction and Raman scattering. Clear evidence of nanofibres structural transformation from pure anatase to pure rutile structures, including the quasi-amorphous and anatase+rutile mixed phases has been confirmed by Raman scattering. By X-ray diffraction was found that the nanofibres crystalline phases present as preferential growth direction (101) for anatase and (110) for rutile. The Raman spectroscopy exhibits the anomalous behaviour for band broadening and shifting of Raman bands with increasing crystallite size that form the nanofibres. The room-temperature photoluminescence presents radiative bands whose main band redshifts, from 2.56 to 1.32 eV, as the crystalline phase transforms in the investigated annealing temperature range.

Thermal Stability of the Structure and Microhardness of the Al–0.05 vol % Al2O3 Nanocomposite Fabricated by Accumulative Roll Bonding

The evolution of the microstructure and microhardness of the Al–0.05 vol % nAl2O3 nanocomposite (where nAl2O3 are aluminum nanoparticles) and aluminum without nanoparticles fabricated by accumulative roll bonding with annealing in a temperature range of 373–573 K is investigated. Ball-shaped Al2O3 nanoparticles with an average diameter of 50 nm are introduced between rolled plates of technically pure aluminum from the first to fourth rolling cycles, while the fifth to the tenth rolling cycles are performed without nanoparticles. The average grain size and aspect ratio of elements of the material grain–subgrain structure in the initial state and after annealing at 473 K are measured using transmission electron microscopy. It is shown that the nanocomposite microhardness is 5–13% higher than the corresponding value of HV for aluminum over the entire studied annealing temperature range. The main factor of the higher nanocomposite microhardness is precipitation hardening due to Al2O3 nanoparticles. The contribution of the substructural and grain-boundary hardening is identical in both materials. The thermal stability of the nanocomposite microhardness is only ~25 K higher than that of aluminum, which is caused by the nonuniform distribution of nanoparticles in the matrix and their low volume fraction. The high thermal stability of the fine-grain structure itself, formed by accumulative roll bonding, when compared with other methods of intense plastic deformation, also plays a role. It is established that most Al2O3 nanoparticles remain at the grain boundaries of nanocomposite after annealing at 473 K; therefore, the ability to fasten the boundary by Al2O3 nanoparticles under the conditions under study is retained at least to 473 K.

Growth characterization of intermetallic compounds at the Cu/Al solid state interface

Cu/Al cold-rolled composite plates were annealed in the temperature range of 573∼773 K. The growth mechanism of intermetallic compounds formed at the Cu/Al solid-state interface was analyzed from the point of view of diffusion kinetics. After annealing, the interfacial reaction layer of the sample consisted of three kinds of intermetallic compound: Al2Cu adjacent to Al, Al4Cu9 adjacent to Cu and AlCu between Al2Cu and Al4Cu9. The formation sequence of the intermetallic layers was Al2Cu, Al4Cu9, and AlCu. The results show that the growth of Al2Cu, Al4Cu9 and AlCu layer were governed by reaction-controlled mechanism in the previous period and by diffusion-controlled mechanism in the latter period in the annealing temperature range of 573 to 773 K, and the higher annealing temperature, the earlier the reaction-controlled stage ends for three kinds of intermetallic compound.